The goal of this research program is to elucidate the interaction between a steroid- sensitive neural circuit and dopaminergic system that mediates, in part, the activation of masculine reproductive behavior. It is unclear how the activating effects of dopamine (DA) relate to the regulation of male sex behavior by testosterone (T). We hypothesize that DA is a part of the biochemical cascade initiated by T that ultimately results in male copulatory behavior and that DA may facilitate male sexual behavior by increasing the behavioral effectiveness of T. A number of recent findings concerning the quail preoptic area (POA) makes this a unique model for these investigations. Some of these findings are: 1. The quail POA contains a sexually dimorphic and T-sensitive nucleus, the medial preoptic nucleus (POM) thus providing a clearly defined morphological definition of an area critical for the action of T on sexual behavior; 2. The T-metabolizing pathways (in particular its aromatization) mediating the activation of behavior have been described; 3. An immunocytochemical (ICC) procedure has been developed which permits visualization of the aromatase-containing cells in the POM; 4. The distribution of the aromatase is sexually dimorphic in the POM along with DA turnover; and 5. There is evidence that aromatase activity in POM is regulated by DA systems. Our experiments are investigating numerous aspects of this model system, including characterizing DA inputs to POA and n. accumbens and correlating behavioral changes with DA-induced T aromatization. These studies should not only enhance our understanding of the neurochemical processes implicated in the control of normal behavior but also provide new insights into many of the pathologies which are sexually differentiated or are simultaneously controlled by the endocrine and neurochemical environments.